/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.transforms.windowing;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.sdk.values.PCollectionView;

import com.bff.gaia.unified.sdk.transforms.ParDo;

import org.joda.time.Duration;



import java.io.Serializable;



/**

 * <b>Experimental! This will be ready for users eventually, but should be considered internal for

 * now. No backwards compatibility guarantees.</b>

 *

 * <p>A function that takes the windows of elements in a main input and maps them to the appropriate

 * window in a {@link PCollectionView} consumed as a {@link

 * ParDo.MultiOutput#withSideInputs(PCollectionView[]) side input}.

 */

@Experimental

public abstract class WindowMappingFn<TargetWindowT extends BoundedWindow> implements Serializable {

  private final Duration maximumLookback;



  /** Create a new {@link WindowMappingFn} with {@link Duration#ZERO zero} maximum lookback. */

  protected WindowMappingFn() {

    this(Duration.ZERO);

  }



  /** Create a new {@link WindowMappingFn} with the specified maximum lookback. */

  protected WindowMappingFn(Duration maximumLookback) {

    this.maximumLookback = maximumLookback;

  }



  /** Returns the window of the side input corresponding to the given window of the main input. */

  public abstract TargetWindowT getSideInputWindow(BoundedWindow mainWindow);



  /**

   * The maximum distance between the end of any main input window {@code mainWindow} and the end of

   * the side input window returned by {@link #getSideInputWindow(BoundedWindow)}

   *

   * <p>A side input window {@code w} becomes unreachable when the input watermarks for all

   * consumers surpasses the timestamp:

   *

   * <p>(end of side input window) + (maximum lookback) + (main input allowed lateness).

   *

   * <p>At this point, every main input window that could map to {@code w} is expired.

   */

  public final Duration maximumLookback() {

    return maximumLookback;

  }

}